The present invention relates in general to the well drilling art and, more particularly, to the art of rotary well drilling.
The conventional practice in rotary well drilling is to install a casing after the well bore has been completed. When drilling through unconsolidated formations, this practice frequently results in lost circulation during drilling, sticking of the drill bit during drilling, sticking of the casing upon insertion thereof into the well bore after completion of drilling, and the like. Occasionally, problems arise which necessitate abandoning the hole and starting over.
The present invention overcomes difficulties of the foregoing nature by installing the casing in the well bore as the hole is being drilled. More particularly, the present invention contemplates a rotary drill bit which is contractible to fit within a casing to permit withdrawal thereof through the casing, and which is expandable below the casing to drill a well bore of a diameter larger than the outside diameter of the casing so as to permit the casing to follow the bit closely during drilling, thereby eliminating such problems as lost circulation, sticking of the drill bit, collapsing of the well bore above the drill bit, and the like. Whenever it is necessary to withdraw the drill bit from the hole to change it, the bit can be contracted readily to permit withdrawal thereof through the casing. In running a new drill bit in, the bit is expanded below the casing to continue drilling a hole larger than the outside diameter of the casing.
Relevant prior art known to me includes the following U.S. patents:
U.S. Pat. No. 1,585,540, Dougherty; U.S. Pat. No. 1,607,791, Dougherty; U.S. Pat. No. 2,193,721, Gunderson; U.S. Pat. No. 2,330,083, Sewell; U.S. Pat. No. 2,705,129, Menton et al; U.S. Pat. No. 2,978,047, De Vann; U.S. Pat. No. 3,077,235, Govin; U.S. Pat. No. 3,545,553, Kammerer, Jr. et. al; U.S. Pat. No. 3,552,508, Brown; U.S. Pat. No. 3,664,755, Carns.
Many of the foregoing patents disclose rotary drilling systems wherein the bit is contractible for withdrawal through a casing or drill string, but wherein the casing or drill string rotates with the drill bit, in most instances to drive it. Such rotation of the casing can result in considerable wear thereof during the drilling operation. In other instances, means must be provided for expanding and/or contracting the bit, such means being run in from the surface whenever expansion or contraction of the bit is desired. Still others utilize cutter arm pivots which are required to carry the drilling load, which is undesirable, and/or utilize a single pivot for a plurality of cutter arms, which is also undesirable.